1. Field of the Invention
This invention relates to an organic conductive medium and an organic photoconductive medium, processes for the preparation thereof and methods for processing them, more particularly to an organic (photo)conductive medium (here, "organic (photo)conductive medium" means "organic conductive medium and organic photoconductive medium", and the prefix "(photo)" is used hereinafter with the same meaning) of which the organic (photo)conductive layer is patterned into high (photo)conductive regions and low- or non-(photo)conductive regions, and also to a process for preparing an organic (photo)conductive medium, which process can provide said organic (photo)conductive medium easily, and a method for processing the same.
2. Related Background Art
Various conductive media such as various IC or semiconductors and various photoconductive media such as photoelectric converting elements, etc. are known in the prior art inorganic material for the most part has been used for the functional portion of these (photo)conductive media. However, as the result of the requirements for higher preciseness, higher fineness, higher integration for these (photo)conductive media, the utility of (photo)conductive organic materials has been widely investigated. Organic materials can be easily handled as the material for the functional portion of semiconductor element, etc. and available in a variety of types.
As one example of conductive organic material, an organic charge transfer complex is known, while as one example of photoconductive organic material, a (photo)conductive organic compound has been known. As the method for forming such (photo)conductive compound as a uniform film on any desired substrate, various methods are known. As one example, the Langmuir-Bloddget method (LB method) proposed by Langmuir et al is known.
According to the LB method, a monomolecular film of a photoconductive organic compound having a hydrophobic site and a hydrophilic site in one molecule or a built-up film thereof can be easily formed on a substrate. The (photo)conductive organic layer thus formed, because hydrophobic sites with high electrically insulating property and the hydrophilic sites with high (photo)conductivity overlap one another in multiple layers in planar shapes, has a peculiar property of anisotropic (photo)conductivity, exhibiting good (photo)conductivity in the horizontal direction of the film, and also having high insulating characteristic in the direction vertical to the film.
The (photo)conductive organic layer as described above has very uniform (photo)conductivity in the planar direction of the layer, and various uses have been demonstrated therefor.
In these organic (photo)conductive media, when used as various electrical elements such as electrical circuits, etc., the (photo)conductive layers is required to be finely processed into desired patterns. As such fine processing method, for example, it may be conceivable to form and grow the (photo)conductive layer as described above into a pattern shape. However, since the LB film as mentioned above is formed by the method in which uniform monomolecular films spread on an aqueous phase are transferred onto a substrate, formation of a film in such pattern shape has not yet been achieved at a practical level.
As another method, it may be conceivable to subject the LB film once formed to patterning by the post-treatment, for example, by etching to remove the desired region of the film. However, this method, as different from chemical etching of an inorganic material, encounters difficulties in selection of the masking material, the masking method, the etchant, etc., posing a problem that the (photo)conductive layer other than the etching region may be denatured. Particularly, as the organic (photo)conductive medium becomes higher in density and integration degree, such fine processing becomes virtually impossible, whereby there is involved the problem that excellent characteristics of the layer comprising the monomolecular film of an organic (photo)conductive compound or a built-up film thereof cannot be fully exhibited.
The LB film as described above has conductivity generally of about 0.1 S/cm and photoconductivity generally of about 10.sup.-10 to 10.sup.-14 S/cm, which are generally very high values for an organic material but are remarkably smaller as compared with gold, silver, copper, etc. which are inorganic conductive materials of the prior art, thus posing the problem that it is insufficient also in aspect of (photo)conductivity.
Accordingly, is been desirable to have a technique for forming a highly precise and fine pattern easily on an organic (photo)conductive medium having the functional portion comprising a (photo)conductive organic material as described above, without impairing the characteristics of these layers.
Also, the photoconductive layer exhibits low wavelength dependency on a photosensitive wavelength, posing the problem that broad photosensitivity is exhibited to a specific wavelength.
Therefore, it has been desirable to have a technique for enhancing photoconductivity and wavelength dependency of the organic photoconductive medium having the functional portion comprising a photoconductive organic material as described above, without impairing the characteristics of these layers.
Also, in case, respective external electrodes required are formed in various electrical elements as mentioned above, when the functional portion of an electrical element is an inorganic material, such electrodes can be readily formed on their surfaces since most of these inorganic materials have conductivity in all the directions, namely they are isotropic materials. However, in the case of an electrical element in which the monomolecular film of an organic charge transfer complex as mentioned above or built-up film thereof is the conductive layer, since these conductive layers have insulting layers and conductive layers overlapping one another in the vertical direction, by only formation of a conductive region for electrodes on the surface, it is difficult to form an Ohmic or Schottky junction due to the presence of the insulating layer forming the layers, whereby no effective external electrode can be formed.
For example, for formation of external electrodes, it is necessary to destroy or peel off the desired portion of the monomolecular film or built-up film thereof in the perpendicular direction and fill a conductor therein. According to such method, since the layer is an organic material and also has a very fine structure, it is very difficult to form accurately the monomolecular film or built-up film thereof. Therefore, the parameters, such as interelectrode distance and electrode area to be formed, influencing greatly the electrical characteristics cannot be controlled with good precision, thereby ensuing the problem that no electrical element of uniform quality can be formed. Particularly, as the electrical element becomes higher in density and integration degree, fine processing can be done with more difficulty, whereby there is the problem that excellent characteristics of the layer comprising a monomolecular film of an organic charge transfer complex or built-up film thereof cannot be fully exhibited.
Accordingly, it has been desirable to have a method for forming easily highly precise and fine external electrodes on the electrical element having the functional portion comprising a conductive organic material as described above, without impairing the characteristics of these layers.